1. Field of the Invention
The present invention relates to a tilting circular table device, and more particularly, a tilting circular table device for use as an attachment to a machine tool.
2. Description of Prior Art
In machining a workpiece by a machine tool, a tilting circular table device is used when rotational dividing operation and tilting dividing operation of the workpiece are required. The workpiece is assembled into a circular table of the tilting circular table device.
A tilting circular table device of this type has such a function as to hold an angle of inclination of a workpiece, in turn, a circular table, while rotating the circular table in case of performing rotational index of the workpiece relative to a machine tool, and to hold a rotational angle of the workpiece, in turn, the circular table, while tilting the circular table in case of performing tilting index of the workpiece. In other words, a tilting table drive motor only tilts, not rotates, the circular table. Also, the circular table drive motor only rotates, not tilts, the circular table.
As one of such tilting circular table devices, there is known a tilting circular table device comprising: a frame; a tilting table supported on the frame so as to rotate angularly; a circular table disposed on the tilting table so as to rotate angularly; an input shaft disposed on the tilting table so as to rotate angularly and rotating the circular table; a circular table drive motor provided with a body portion disposed on the frame; a rotation transmitting mechanism for transmitting rotation of an output shaft of the circular table drive motor to the input shaft; and the tilting table drive motor for angularly rotating the tilting table (Patent Document 1).
The rotation transmitting mechanism of this tilting circular table device includes a differential mechanism, whose differential characteristic is set such that, while the circular table drive motor is stopped, the differential mechanism rotates the input shaft synchronously in the same direction by the rotational angle, if the tilting table is angularly rotated by the tilting table drive motor, but while the tilting table drive motor is stopped, the differential mechanism rotates the input shaft only, if the input shaft is angularly rotated by the circular table drive motor.
This tilting circular table device has the tilting table drive motor and the circular table drive motor disposed on the frame and drives the circular table by the circular table drive motor through the differential mechanism having a proper differential characteristic, thereby tilting the circular table without rotating it or rotating the circular table without tilting it.
In the foregoing conventional tilting circular table device, however, since the differential mechanism inside the frame combines each rotation axis and gear of the circular table and the tilting table so that a predetermined gear ratio can be obtained, which makes the structure inside the differential mechanism complicated. As a result, when the differential mechanism is broken, a great deal of labor is required for reparation of the broken differential mechanism as well as for maintenance of the differential mechanism.
Furthermore, in the conventional tilting circular table device, since the differential mechanism has a lot of gears, it is impossible to avoid backlash generating among those meshed gears. Due to this, when the differential mechanism converts the rotational direction of the output shaft of the circular table drive motor or of the tilting table drive motor from one to the other, a range where the rotation is not transmitted due to the backlash is expanded. As a result, if the differential mechanism using a lot of gears is applied to a machine tool for which fine and accurate angular control of a circular table and a tilting table is required, accuracy in angle of angular rotation of the circular table and the tilting table cannot be improved.
[Patent Document 1] Japanese Patent No. 2793849 Official Gazette